The prior art is replete with efforts to modify polymeric materials for optimal use as molding compounds. These efforts are generally directed toward obtaining molded articles having good thermo-mechanical properties such as tensile strength, impact resistance, heat distortion temperature, and flame resistance.
Thermosetting unsaturated polyester resin based molding compounds are well known in the art. These compounds usually consist of an unsaturated polyester resin, an ethylenically unsaturated copolymerizable monomer, inert fillers, reinforcing fibers, and a catalyst. Polyester molding compounds are described in U.S. Pat. Nos. 3,940,350; 3,974,124; 3,227,665; 3,701,748; 3,948,716, and 4,101,604. The U.S. Pat. No. 4,101,604 specifically describes a molding composition containing unsaturated polyester resin, polymerizable monomers, and epihalohydrin polymers used as tougheners. A severe disadvantage with polyester based compositions and articles made therefrom is their relatively low flame resistance properties. It is also well known that thermosetting resins such as polyesters are relatively brittle to fabricate when compared to thermoplastic materials such as polyvinyl chloride.
Because of their ease of fabrication, there has been a greatly increased demand for thermoplastic molding compositions. The most available and one of the least expensive of all general purpose thermoplastics is polyvinyl chloride. Various compositions which contain polyvinyl chloride resins are disclosed in U.S. Pat. Nos. 2,943,952; 3,066,110; 3,700,624; 3,557,046; 3,275,714; and 3,305,514. The U.S. Pat. No. 3,700,624 describes a resinous composition comprising a vinyl chloride resin, an unsaturated polyester resin, an acrylic acid ester plasticizer and a polymerization initiator. The U.S. Pat. No. 3,275,714 describes reinforced plastic compositions composed of a thermoplastic resin, such as polyvinyl chloride; a thermosetting synthetic polymer, such as epoxide resin or an unsaturated alkyl resin; a polymerizable polyalkenyl monomer; a polymerizable monoalkenyl monomer; and a randomly dispersed reinforcing fiber. These compositions are stated to possess the ease of fabrication of thermoplastics combined with the high performance of thermosetting plastics in the end product.
The cured prior art compositions comprising polyvinyl chloride, unsaturated polyester resin or epoxy resin, and polymerizable monomers are basically a fused matrix which has unreacted polyvinyl chloride dispersed therein. Several advantages are obtained from the compositions of the present invention which results in a reactive polyvinyl chloride which is firmly bonded to the polymeric matrix upon curing and forming an interpenetrating polymer network (IPN). The present invention results in a cured composition which is transparent and has a single glass transition temperature as opposed to the multiple glass transition temperatures of the prior art compositions. In addition, the compositions of the present invention result in a significant improvement in thermo-mechanical properties. Further, the present invention results in compositions which possess the ease of fabrication of thermoplastics with the stability and durability of thermosets, and which are flame resistant.
The compositions of this invention find utility in conventional sheet molding, bulk molding, compression molding, and injection or extrusion molding applications. The glass fiber containing compositions are particularly useful in sheet molding and bulk molding operations.